This invention relates to dies for extrusion blow-molding equipment, particularly dies which are usable for producing multi-layered parisons which are blow-molded into containers, methods of forming such containers and the tubular extrudate and to the parisons and containers themselves.
One patent of interest in this regard is U.S. Pat. No. 4,522,755 issued June 11, 1985, incorporated by reference herein, which discloses an extrusion blow-molding die for use in producing multi-layer tubular parisons which are then blown into bottles and other containers, methods of forming such containers and the containers themselves. Parisons are formed having multiple layers, including a scrap layer, and an oxygen barrier layer. U.S. Pat. No. 4,522,775 refers to U.S. Pat. Nos. 3,560,325, 3,595,740, 3,882,259, 3,955,697, 4,182,457, 4,234,663 4,047,868, 4,297,092, 3,802,826, 3,447,204, 3,478,139, 3,546,743, 4,042,661, 4,125,585, 4,134,952, 4,152,104, 4,042,661, 3,446,204, and 4,079,850 which are incorporated herein by reference.
U.S. Pat. No. 3,457,337, issued to Turner, discloses containers having a layer Ms in FIG. 3 and L2 in FIG. 5, which layer extends partially, but not totally, throughout the containers. These containers do not have a scrap layer. In the present invention, by contrast, all layers extend throughout the container, and the containers include a layer containing regrind of the parison scrap or "flash", which scrap or flash contains less than all of the layers of the parison portion used to make the container. Turner also discloses in FIG. 1, "valves" V1 and V2 in schematic form with no teaching of the construction thereof. Apparently, such valves progressively or gradually interrupt the flow of resin L2 between the extruder and the die. By contrast, as explained in detail herein, this invention is in specific apparatus and method for controlling and terminating resin flow operating within the die head itself.
The control of resin flow at the extruder, as opposed to within the die head, is also disclosed in U.S. Pat. No. 4,276,250 to Satchell et al. See also U.S. Pat. No. 3,023,461 to Sherman and Haines Reissue U.S. Pat. No. 24,577 which are directed to a different object, namely, control of thickness of the parison.
One aspect of the present invention is directed to the same general object as the aforesaid U.S. Pat. No. 4,522,755, namely, the continuous extrusion of tubular multi-layered parisons However, in the U.S. Pat. No. 4,552,755, the parison formed by the dies therein contain the same materials in all layers throughout the parison, i.e., not only in the parison portions that are encaptured within the molds and blown into the container, but also in the portions of the parison between the molds which are the "flash" or scrap. As is well-known, after the overall parison is formed, it is thereafter passed into one or more molds of a blow-molding machine, and the portions of the parison beyond or outside of the mold or between spaced-apart mold sets, which are not encaptured by the mold itself, are scrap. In the U.S. Pat. No. 4,522,755, however, method and apparatus and process were disclosed whereby such scrap can be utilized and fed back into the die as a layer, thereby reducing wastage of the scrap.
Another patent of interest is U.S. Pat. No. 4,149,839 (Iwawaki et al.) which discloses a multi-polymer stream extrusion die head for intermittently extruding, by positive displacement, a plurality of polymer materials to form parisons having portions with all of the materials introduced into the extruder die head and portions having less than all of such materials present. The apparatus utilizes the movement of a plurality of reciprocable ring pistons in the die head to regulate the flow of one or more of the polymer materials. More particularly, a ring piston is withdrawn in a direction opposite to the direction of flow to control or interrupt downstream movement of polymer material alongside or past the ring piston, to thereby terminate flow of said material from the die head. Contrary to the invention disclosed herein, the U.S. Pat. No. 4,149,839 does not disclose that any ring piston surface abuts or contacts a die member surface and another surface or structure formed by and between those contactive surfaces, to thereby shut-off or close-off resin flow through a channel.
The U.S. Pat. No. 4,149,839 also does not disclose the lack of die wall contact downstream of the resin combining or merge area beyond the contact point between contacting surfaces. The March 1977 issue of Modern Plastics, "Coextrusion-blow Molding For Gas Tanks and Industrial Parts", pg. 70 et seq., written by some of the inventors of the U.S. Pat. No. 4,149,839, discloses a coextrusion blow-molding accumulator having independent ring-piston rams for regulating component layer thickness from 0 to 100% of total thickness in multi-layer parisons, thereby making it possible to abruptly terminate one or more of the individual layers when desired and to obtain single resin trim for recycling. As disclosed in the publication, the ring piston rams are withdrawn to a point above the infeed port from the extruder while the rein channel is being recharged, and ring piston movement during extrusion is downward to a point just above the feed port orifice. In either the patent or the publication, there is no disclosure that the ring piston rams are moved further downward beyond that point to shut-off or close-off flow of resin from the feed port orifice.
It would be highly desirable in a continuous or intermittent extrusion blow-molding process or apparatus to be able, and it is an object of this invention, to selectively eliminate from the scrap portions of a parison, to the extent practically possible, one or more materials or one or more layers, especially those comprised of relatively expensive materials (e.g., a polyvinylidene chloride copolymer such as Saran or a methyl acrylate Saran, a "Saran", an ethylene vinyl alcohol polymer or copolymer containing (EVOH), etc.). Even if the scrap containing the thermally unstable materials "or" relatively expensive layers is recycled back into the die, it is less expensive to produce containers having flash or scrap with substantially less or none of such expensive layers. For example, oxygen barrier materials, such as EVOH, are currently used on a commercial basis by the Assignee hereof, and EVOH, relatively speaking, is a very expensive material. Accordingly, from a commercial standpoint, it is very desirable in this type of technology to have the capability to substantially eliminate from the scrap portions of the parison such expensive materials or layers, whether such scrap portions are to be recycled or not.